1. Field of the Invention
The present invention relates to a structure and method for detecting an inflated state of a dam formed by a flexible membrane disposed in a culvert, with the flexible membrane being inflated due to fluid being supplied thereto and being deflated due to fluid being discharged therefrom.
2. Description of the Related Art
Conventionally, a dam formed by a flexible membrane has been used as a sluice gate disposed in a conduit (such as a sluice pipe) crossing a levee, and as an adjusting gate or a checking gate disposed in a culvert such as a sewage pipe or a water conduit.
When fluid (such as air or water) is supplied inside the flexible membrane, the flexible membrane is inflated to close watercourses such as a river. When the fluid is discharged, the flexible membrane is deflated to open the watercourses.
Because the flexible membrane dam is disposed inside the conduit or the like and cannot be seen from the outside, sometimes a pressure detector is used to determine whether the flexible membrane dam has been completely inflated by detecting whether pressure within the flexible membrane has reached a specified value. However, there are cases in which the pressure detector cannot accurately detect that the flexible membrane has actually been completely inflated due to slight errors in the pressure detection.
In view of this drawback, an alternative structure shown in FIGS. 10A and 10B has been suggested (see Japanese Patent Application Laid-Open No. 2001-20263), in which a diaphragm-type pressure detector 116 is mounted on a ceiling 114 of a conduit 112. When a flexible membrane 118 has been completely inflated, the flexible membrane 118 contacts the ceiling 114, and a compressive force is exerted on the pressure detector 116 by air pressure inside the flexible membrane 118. The diaphragm of the pressure detector 116 is thereby deformed, and the deformation of the diaphragm is electrically detected by the pressure detector 116. In this manner, whether the flexible membrane 118 has been completely inflated can be remotely verified in a handling room 120.
However, when a compressive force exerted on the diaphragm is used to detect the fully inflated state of the flexible membrane 118, accurate detection is problematic because the diaphragm is also presumably distorted by water pressure or the like when the flexible membrane 118 is deflated.
In view of the above facts, it is an object of the present invention to obtain a structure and method that can detect with greater accuracy an inflated state of a flexible membrane dam and are unaffected by pressure resulting from fluid flow when the flexible membrane is not completely inflated.
In accordance with a first aspect of the present invention, a structure for detecting an inflated state of a dam formed by a flexible membrane disposed in a culvert, with the flexible membrane being inflated due to fluid being supplied thereto and being deflated due to fluid being discharged therefrom, the structure comprises: a metal member mountable on the flexible membrane; and a metal detector for detecting the metal member, the metal detector being mountable in the culvert at a position corresponding to the metal member when the flexible membrane has been inflated.
When the flexible membrane is inflated due to fluid being supplied thereto, the metal member disposed on the flexible membrane moves toward the culvert. Since the metal detector is mounted in the culvert at the position corresponding to the metal member when the flexible membrane has been inflated, the metal detector detects the metal member when the flexible membrane has been completely inflated. In this manner, the metal detector detects the metal member, whereby the inflated state of the flexible membrane dam can be detected. Since this structure detects the inflated state thereof without conventionally detecting pressure, the inflated state can be accurately detected without being affected by fluid pressure.
As the metal detector, any commonly used conventional metal detector can be used.
In accordance with the first aspect of the present invention, the metal member is usually disposed at a substantial center of the flexible membrane when viewed in a direction in which the flexible membrane inflates.
The center of the flexible membrane is moved in a large amount when the flexible membrane is inflated and deflated. Therefore, the metal member is disposed at the center (when viewed in the inflation direction) of the flexible membrane, whereby the inflated state can be more accurately detected.
In accordance with the first aspect of the present invention, the metal member is usually a tabular metal plate.
The metal member may be spherical, rectangular parallelepiped, block-shaped, etc. However, when the metal member is tabular, protrusion from the flexible membrane can be reduced.
In accordance with the first aspect of the present invention, the structure further usually comprises a covering member for covering at least part of the metal member.
Accordingly, at least the portion of the metal member that is covered with the covering member can be protected. The metal member may be completely covered with only the covering member, or with both the covering member and an additional cloth member, so that the metal member can be more reliably protected.
In accordance with the first aspect of the present invention, the metal member is usually not attached to the flexible membrane.
When the fluid is supplied, the flexible membrane extends/contracts in its directions. If the metal member is not attached to the flexible membrane, the metal member remains unaffected by distortion of the flexible membrane. In the structure including the covering member, when the flexible membrane extends/contracts, the covering member may also extend/contract. In this case, similarly, if the metal member is not attached to the covering member, contact between the metal member and the covering member is unaffected by distortion of the flexible membrane.
In accordance with the first aspect of the present invention, a periphery of the covering member usually tapers away from a center of the covering member.
Accordingly, when the flexible membrane has been completely inflated, a clearance generated between the flexible membrane and the culvert is reduced (preferably eliminated), and occlusion of the culvert is improved.
When the flexible membrane is deflated, an area thereof opposing the direction that the fluid flows in the culvert is reduced (preferably eliminated). Therefore, foreign substances flowing together with the fluid are not often caught, and durability of the covering member is improved.
In accordance with the first aspect of the present invention, an outer edge of the covering member outwardly extrudes from that of the metal member usually by 100 mm or more.
Accordingly, the metal member can be completely covered with only the covering member, or with both the covering member and the additional cloth member. Further, the portion of the covering member that outwardly extrudes from the metal member can be securely attached to the flexible membrane.
In accordance with the first aspect of the present invention, the covering member usually comprises a thickness within a range of from 2 mm to 10 mm.
When the thickness of the covering member is at most 10 mm, the amount of protrusion from the flexible membrane can be reduced. When the thickness is at least 2 mm, the strength of the covering member can be obtained.
In accordance with the first aspect of the present invention, a covering unit that includes the metal member and the covering member is usually attached to the flexible membrane.
Accordingly, if the covering unit has been produced in a factory, only attachment of the covering unit to the flexible membrane is needed on a site, and thus, execution property thereof is improved.
In accordance with the first aspect of the present invention, a cloth member for covering at least some corners of the metal member is usually mountable between the metal member and the covering member.
Accordingly, loads applied from the corners of the metal member to the covering member are eased by the cloth member, and the covering member can be prevented from being damaged.
In accordance with the first aspect of the present invention, at least some corners of the metal member are usually chamfered so as to have a predetermined curvature.
Accordingly, even if the corners of the metal member contact the covering member, local loads are reduced by the chamfered portions, and the covering member can be prevented from being damaged.
The chamfered portions may be formed, for example, by chamfering the corners of the metal plate viewed in a normal direction, or by rounding ends (edges) of the metal plate in a thickness direction viewed in the thickness direction.
In accordance with the first aspect of the present invention, the metal plate is usually substantially circular.
Since the entire periphery of the circular metal plate has a predetermined curvature, the covering member can be reliably prevented from being damaged. Further, orientation of the circular metal plate does not need to be considered when the circular metal plate is disposed on the flexible membrane.
In accordance with the first aspect of the present invention, the metal plate is usually substantially elliptical.
Since the entire periphery of the elliptical metal plate may have a predetermined or smaller value of curvature, the covering member can be reliably prevented from being damaged. Further, if the position of the elliptical metal plate is deviated when the flexible membrane is inflated, the elliptical metal plate can be disposed so that effect of the deviation is reduced. For example, when the flexible membrane is pressed by fluid flow in the culvert, the center position of the flexible membrane may shift downstream. Therefore, if the elliptical metal plate is disposed so that a longitudinal direction thereof corresponds to the flow direction, the effect of the shift is reduced (preferably eliminated), and the elliptical metal plate can be reliably detected by the metal detector.
The xe2x80x9cellipticalxe2x80x9d shape widely includes a general ellipsoidal shape, a substantially ellipsoidal shape in which semicircles are continuously connected to ends of two parallel lines, and a shape in which curvatures at ends of a major axis or a minor axis are different from each other (so-called xe2x80x9covalxe2x80x9d shape).
In accordance with the first aspect of the present invention, the metal plate comprises an outside dimension within a range of from 50 mm to 1,000 mm.
When the outside dimension of the metal plate is at least 50 mm, the metal plate can be reliably detected by the metal detector, and when the outside dimension is at most 1,000 mm, distortion applied to the metal plate when the flexible membrane is inflated can be reduced, and increase of weight of this structure can be restricted.
In accordance with the first aspect of the present invention, the metal plate comprises a thickness usually within a range of from 2 mm to 10 mm.
When the thickness of the metal plate is at most 10 mm, the amount of protrusion from the flexible membrane can be reduced. When the thickness is at least 2 mm, the strength of the metal plate can be obtained.
In accordance with the first aspect of the present invention, the metal member usually comprises rust-proofing. Accordingly, the metal member can be prevented from rusting.
A second aspect of the present invention is a method for detecting an inflated state of a dam formed by a flexible membrane disposed in a culvert, the method comprising the steps of: (a) disposing a metal member on the flexible membrane; (b) mounting a metal detector on an inner surface of the culvert; and (c) adjusting a position of at least one of the metal member and the metal detector so that the metal detector detects the metal member only when the flexible membrane has been inflated.